In liquid crystal display devices, optical members such as a phase difference film are used in order to improve performance. When the phase difference film is used for antireflection for mobile devices, organic EL television and the like, and optical compensation for the liquid crystal display device, a slow axis of the phase difference film is required to be in an angle neither parallel nor perpendicular to the transmission axis of a polarizer. In contrast, the transmission axis of the polarizer is usually in parallel with the long side direction or the short side direction of the rectangular display face of the device. Consequently, a rectangular phase difference film having a slow axis in a diagonal direction to the sides of the phase difference film is required.
Conventionally, a phase difference film has been produced by lengthwise stretch or transverse stretch of a long-length pre-stretch film. Here, the lengthwise stretch means the stretch of the long-length film in a longitudinal direction and the transverse stretch means the stretch of the long-length film in a width direction. In order to obtain the rectangular phase difference film having the slow axis in a diagonal direction from such a long-length film, the phase difference film is required to be cut out so that the sides of the phase difference film face in a direction diagonal to the width direction of the long-length film. Such production, however, increases the amount of discarded films or causes difficulty in roll-to-roll production, and therefore, the production efficiency becomes low.
Consequently, it has been suggested that a long-length pre-stretch film is stretched in a diagonal direction in order to improve the production efficiency (refer to Patent Literatures 1 to 5).